JP3355102B2 - Positive active material for lithium secondary battery and secondary battery using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode active material for a lithium secondary battery and a secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, miniaturization and high performance of cordless electronic devices have progressed, and attention has been paid to secondary batteries (storage batteries capable of charge / discharge cycles) as drive power sources for these devices. Expectations are high for batteries with high voltage and high energy density.

As a positive electrode active material of such a battery, a layered compound capable of intercalating and deintercalating lithium, for example, LiCoO ₂ or L
A composite oxide mainly composed of Li and a transition metal such as iNiO ₂ (hereinafter referred to as lithium composite oxide) is used. That is, in order to produce a lithium composite oxide, for example, LiNiO ₂ , a mixed powder obtained by mixing a Li salt and a Ni compound is prepared by mixing 75 powders.
It can be synthesized by firing at a temperature of about 0 ° C. for a predetermined time in an oxygen stream.

The above-described method has been devised to develop a Li-intercalation type crystal structure, facilitate the movement of Li ions, and increase the battery capacity.

[0005]

However, the conditions for obtaining a crystal structure for initially increasing the capacity of a Li secondary battery are as follows:
For example, starting materials and firing conditions have been studied, but no study has been made on the elements that hinder the development of the crystal structure.Moreover, in order to make it difficult for the capacity to decrease even when a charge / discharge cycle is performed in a high-temperature environment. It is disclosed in Japanese Patent Application Laid-Open No. HEI 5 (1993) -510 that a lithium composite oxide serving as a positive electrode active material has a proper particle size distribution.
According to Japanese Patent Application Laid-Open No. 15-1998, it is disclosed in Japanese Unexamined Patent Application Publication No.
However, there are few effective countermeasures for suppressing a decrease in capacity during storage as a secondary battery.

Conventionally, Li which has a high initial capacity and excellent storage stability
Although the synthesis of CoO ₂ powder was relatively easy, LiNi
O ₂ powder or LiNi _1-x M _x O ₂ powder [where 0 <
x ≦ 0.4, M = Co, Mn, B, Al, V, P, M
g, Ti).
LiNiO ₂ or LiNi _1-x M _x O ₂ powder [where 0 <x
≦ 0.4, M = Co, Mn, B, Al, V, P, Mg,
Powder of Ti) is poor in the reproducibility of the initial capacity, and the secondary battery using these powders has a large decrease in capacity during storage.

Accordingly, an object of the present invention is to provide a positive electrode active material for a lithium secondary battery, which is expected to have an initial high capacity when incorporated in a secondary battery, or which suppresses a decrease in capacity during storage, and a battery therefor. And a secondary battery using the same.

[0008]

Means for Solving the Problems As a result of research to achieve the above object, the present inventors have found that when a sulfur component mainly introduced from a starting material in a lithium composite oxide serving as a positive electrode active material exceeds a certain amount. it causes a decrease in the initial capacity of the battery becomes an impediment to the crystal structure development of the composite oxide, also the specific surface area of the composite oxide from the viewpoint of the storage stability of the battery is small moderately, whereas 0.5 m ² / When the amount exceeds g, it was found that the reactivity with the electrolytic solution was increased and the capacity during storage was reduced, and the present invention was reached.

That is, the present invention firstly provides LiNiO ₂
Powder or LiNi _1-x M _x O ₂ powder [0
<X ≦ 0.4, M = Co, Mn, B, Al, V, P, M
g, one or more of Ti] in which the sulfur content is 0.5% by weight or less. Secondly, LiNiO ₂ powder or LiNi _1-x
M _x O ₂ powder [where 0 <x ≦ 0.4, M = Co, M
at least one of n, B, Al, V, P, Mg, and Ti] and the powder has a specific surface area of 0.06 to 0.46 m ² / g. Thirdly, the positive electrode active material for a lithium secondary battery according to the first or second item, wherein the sulfur content is 0.01% by weight or less: Fourth, LiNiO ₂ powder having a sulfur content of 0.5% by weight or less or LiNiO ₂ powder
Ni _1-x M _x O ₂ powder [where 0 <x ≦ 0.4, M
= At least one of Co, Mn, B, Al, V, P, Mg, and Ti] as a positive electrode active material, and incorporating a positive electrode mixture obtained by kneading a conductive agent and a binder. Fifth, the lithium secondary battery has a sulfur content of 0.5% by weight or less and a specific surface area of 0.06 to 0.46 m.
² / g LiNiO ₂ powder or LiNi _1-x
M _x O ₂ powder [where 0 <x ≦ 0.4, M = Co, M
at least one of n, B, Al, V, P, Mg, and Ti] as a positive electrode active material, and incorporating a positive electrode mixture obtained by kneading a conductive agent and a binder. Lithium secondary battery: Sixth, the sulfur content is 0.01% by weight.
The present invention provides the following lithium secondary battery according to the fourth or fifth aspect.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Lithium in a battery moves in the form of ions or complexes, escapes from the positive electrode active material during charging, inserts into the negative electrode through the electrolyte and electrolyte, and reverses during discharging. Is generated.

The active material powder forms primary particles or secondary particles in which the primary particles are aggregated.
iNiO ₂ crystal particles. Therefore, the lithium in the primary particles undergoes solid diffusion movement in the state of ions in the intercalated layer of the crystal lattice during charge and discharge.

According to the study of the present inventors, lithium composite oxide particles having a high sulfur content are hindered in the course of crystal development, do not have a sound crystal structure, and conversely have a low sulfur content. The powder particles have a sound crystal structure. Sulfur is rarely mixed in the middle of the manufacturing process, and is almost always present from the starting material, and it is difficult to remove it by heat treatment. Or it must be sufficiently removed by washing. For cleaning, general cleaning methods can be applied, such as decantation, Nutsche,
Natural filtration by a Buchner funnel, suction filtration, filtration by a filter press, a centrifuge, or the like can be used, but other devices and methods may be applied.

In the present invention, L having a sulfur content of 0.5% by weight or less is used.
The iNiO ₂ powder is used when the content exceeds 0.5% by weight.
This is because the phases are confirmed and the capacity is reduced when incorporated into the battery.

According to the study by the inventors, the larger the specific surface area of the lithium composite oxide powder, the more contact with the electrolytic solution and the remarkable decrease in capacity during storage, so the upper limit depends on the reactivity with the electrolytic solution. Is set to 0.5 m ² / g, and the particle size at this time varies depending on the starting material and the firing conditions, but is approximately 5 to 10 μm as a laser average particle size.
As for the preservability, the smaller the specific surface area, the better, but there is a limit by itself, and the lower limit is 0.01 m ² / g.

It should be noted here that when a raw material containing a small amount of sulfur is used, the reactivity between the lithium compound and the nickel compound is better than when the raw material containing a large amount of sulfur is used. Promoted to increase the primary particle size and reduce the specific surface area.

As the additive element M for improving battery characteristics,
Co, Mn, B, Al, V, P, Mg, Ti, etc. may be mentioned, and these may be combined as needed.
The reason for setting the range of x to 0 <x ≦ 0.4 is that as much as 40% is sufficient as an additive element for improving various characteristics as a battery.

As described above, for example, LiNiO ₂ powder or LiNi _1-x M having a reduced sulfur content and a reduced specific surface area
_x O ₂ powder [where 0 <x ≦ 0.4, M = Co, Mn,
B, Al, V, P, Mg, Ti] is a positive electrode active material having a high capacity and excellent storage stability when incorporated in a battery.

Although the specific surface area can be reduced even when the sulfur content is high, it is necessary to raise the firing temperature or extend the firing time, which leads to the collapse of the crystal structure and the reduction of the capacity at a high temperature. It is disadvantageous in terms of cost in industrialization.

The conditions for producing the positive electrode active material in the present invention will be described. As raw materials, Li, Ni, Co, Mn,
Oxides such as B, Al, V, P, Mg, and Ti, hydroxides, inorganic acid salts, and organic acid salts can be used. Compounds produced by eutectoid precipitation or similar techniques can also be calcined. For mixing, a mixer with a stirrer (attritor, free-type mixer, concrete mixer) or a rotary container type (pot mill, V-type mixer) can be used, but other types of machines may be used.
It is fired through a process such as molding as a raw material mixture. The following method can be used for molding, but other methods may be used depending on the shape. (A) Press (uniaxial press, tablet press, hydrostatic press, vibratory press), (B) Roll briquetter,
(C) an extruder, (D) a rolling granulator. The shape of the molded body is a sphere,
Lenses, rods, plates, and noodles can be manufactured by general techniques, but other shapes are also possible. Firing conditions are 800 ~
The holding time at 1000 ° C. is not particularly limited, but the heat treatment is preferably performed for about 2 to 15 hours in an oxidizing atmosphere (including oxygen + nitrogen and air) in an oxygen stream at atmospheric pressure to 10 atm. Here, the pressure may be higher than the atmospheric pressure on the low temperature side of about 800 ° C., but is preferably higher on the high temperature side, and may exceed 10 atm if possible on the apparatus.

Since the Li content in the raw material is volatilized by baking at about 0.3%, it may be corrected at the time of weighing. In addition, the appearance after baking has a black mass, which is broken up. The required particle size is obtained by classification. Also L
The same effect can be obtained as long as the component ratio of i to other cations is in the range of 1 ± 0.05 / 1 even if the molar ratio is not 1/1.

The obtained LiNiO ₂ powder or LiN
i _1-x M _x O ₂ powder [where 0 <x ≦ 0.4, M = C
o, Mn, B, at least one of Al, V, P, Mg, Ti]
The sulfur content in the sample is measured by a method according to JIS Z2616 infrared absorption method, and the specific surface area is determined by a BET method (Brunauer, Emmet & T
eller method).

For the production of the battery, LiNiO ₂ or LNiO ₂
iNi _1-x M _x O ₂ powder [where 0 <x ≦ 0.4, M =
At least one of Co, Mn, B, Al, V, P, Mg, and Ti] as a positive electrode active material, graphite as a conductive agent, and polytetrafluoroethylene (PTFE) as a binder at a weight ratio of 87: 8: The mixture was kneaded at a ratio of 5 and formed and rolled.

Hard carbon was used for the negative electrode, a polypropylene film cut out of a polypropylene was used for the separator, and ethylene carbonate and diethylene carbonate were used as the electrolyte.
A solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / l as an electrolyte in a liquid mixed at a volume ratio of one to one was used. FIG. 1 shows a schematic cross-sectional view of an example of the test battery prepared as described above. In the figure, 1 is a stainless steel case, 2 is a gasket, 3
Is a sealing plate, 4 is a negative electrode, 5 is a positive electrode, 6 is a separator, 7
Denotes a negative electrode current collector, and 8 denotes a positive electrode current collector. Battery tests in the following Examples and Comparative Examples were performed using this battery.

The charge / discharge test was performed at a current density of 0.5 mA / cm ² , and charging to 4.2 V and then discharging to 2.7 V were repeated three times, and the first discharge capacity was used as the initial discharge capacity. The third discharge capacity was defined as the capacity before storage, and after 2 weeks at 60 ° C., charge and discharge were repeated three times under the same conditions as before storage, and the third discharge capacity was defined as the capacity after storage.

Hereinafter, the present invention will be described in detail with reference to examples.
The scope of the present invention is not limited to these.

[0026]

Example 1 Ni (NO ₃ ) ₂ .6H ₂ O as Ni raw material
And NaOH by a neutralization reaction, and the obtained precipitate was subjected to 2 to 1 kg of Ni (OH) ₂ using a Buchner funnel.
After washing with water at a rate of 0 liter to obtain Ni (OH) ₂ powder, the element S in the powder was measured.
% By weight or less. Next, this Ni (OH) ₂ powder and LiOH · H ₂ O powder as a Li material are mixed so that the molar ratio of Li / Ni is 1/1, and the mixture is molded by a die press under a pressure of 1 t / cm ^2. Into pellets.

The pellets were fired at 800 ° C. for 2 hours in a pure oxygen stream at 1 atm and then pulverized to obtain LiNiO ₂ powder. When the element S of the obtained powder was measured, it was 0.01
% By weight or less. After using this LiNiO ₂ powder as an active material, a conductive material and a binder were mixed and formed into a positive electrode mixture, and incorporated into a battery to evaluate the battery capacity, Table 1 shows the results.

[0028]

As Example 2 Ni raw material NiSO ₄ · 6H ₂ O and Na
Except for changing the degree of washing of Ni (OH) ₂ powder synthesized by neutralization reaction from OH and preparing three types of Ni (OH) ₂ powder, the steps were performed in the same manner as in Example 1, and the initial capacity of the battery was changed. Are shown in Table 1.

[0029]

Comparative Example 1 As in Example 2, NiSO was used as a Ni raw material.
₄ · 6H ₂ O and Ni synthesized by neutralization reaction from NaOH
Regarding the (OH) ₂ powder, a LiNiO ₂ powder was formed in the same manner as in Example 2 except that a powder having a reduced degree of washing was used, and the element S was determined to be 0.57% by weight. Table 1 shows the results of examining the initial capacity of a battery using this powder.

[0030]

[Table 1]

[0031]

Embodiment 3 Ni (NO ₃ ) ₂ .6H ₂ O as Ni raw material
Ni (OH) ₂ synthesized by neutralization reaction with NH ₄ OH
After mixing the powder and LiOH · H ₂ O powder as a Li raw material such that the molar ratio of Li / Ni is 1/1,
It is formed into a pellet by pressing at a pressure of ² t / cm ² by a die press.
Each of the three types was heated at 6 ° C. for 10 hours in a pure oxygen stream at 10 ° C. and crushed to obtain three types of LiNiO ₂ powder. The specific surface areas of these LiNiO ₂ powders were measured, and the storage rates of batteries using them were examined. The results are shown in Table 2.

[0032]

Comparative Example 2 Ni and Li obtained in the same manner as in Example 3.
Example 3 except that the raw materials were fired at 750 ° C. for 10 hours.
LiNiO ₂ powder was obtained in the same process as described above. Table 2 shows the specific surface area and the storage rate in the same manner as in Example 3.

[0033]

Comparative Example 3 As in Example 3, Ni (NO ₃ ) ₂ .6H ₂
Ni (OH) ₂ powder obtained from O and NH ₄ OH and Li
A LiNiO ₂ powder was obtained in the same manner as in Example 3, except that the powder was fired at 860 ° C. for 10 hours using (OH) ₂ powder and then pulverized. Table 2 shows the specific surface area and the storage rate.

[0034]

[Table 2]

[0035]

Example 4 A Ni (OH) ₂ powder was obtained in the same manner as in Example 1, and this powder was mixed with LiOH · H ₂ O powder to obtain 2
Pellets are produced at a pressure of t / cm ² ,
The mixture is calcined at 3 atm in a pure oxygen stream for 10 hours and then pulverized to obtain a LiNiO ₂ powder. When the element S and the specific surface area of this powder were measured, S was 0.01% by weight or less and 0.11 m ^2.
/ G. Further, the battery characteristics were examined by incorporating the battery into a battery. The results are shown in Table 3.

[0036]

Example 5 Ni (OH) ₂ obtained in the same manner as in Example 4.
In a molding method using powder and LiOH.H ₂ O, H ₂ O is mixed and kneaded, and a LiNiO ₂ powder is obtained in the same manner as in Example 4 except that the mixture is extruded from a hole having a diameter of 5 mm and molded.
Table 3 shows the results of examining the battery characteristics.

[0037]

Embodiment 6 In the same manner as in Embodiment 2, NiSO ₄ .6H ₂ O
After sufficiently washing Ni (OH) ₂ powder obtained from NaOH and NaOH in the same manner as in B of Example 2, the subsequent steps were performed in the same manner as in Example 4 to obtain LiNiO ₂ and similarly battery characteristics. Table 3 shows the results of the evaluation.

[0038]

Comparative Example 4 LiNiO ₂ powder was obtained in the same manner as in Example 6 except that Ni (OH) ₂ powder was obtained in the same manner as in Example 6, and this powder was not sufficiently washed as in Comparative Example 1.
A powder was obtained. Table 3 shows the results of examining battery characteristics by incorporating the powder into a battery.

[0039]

Comparative Example 5 Ni (OH) ₂ obtained in the same manner as in Example 4.
Using powder and LiOH · H ₂ O powder at 900 ° C.
After calcination for a period of time, Li
Table 3 shows the results obtained by obtaining NiO ₂ powder and similarly examining the battery characteristics.

[0040]

[Table 3]

[0041]

EXAMPLE 7 Tables 4 and 5 show the results obtained by examining whether similar effects can be obtained by further adding various elements. However, the additive element shows two cases, the case of coprecipitating with the Ni compound and the case of mixing with the Ni compound. The generation of the precipitate and the washing are P, R, S, T, U, W and Y are the same as those in Example 1. Similarly,
Q, V, X, and Z were the same as those in Example 2B. For firing and the like, R was 900 ° C. for 15 hours.
Similarly to the above, the pressure was measured under the conditions shown in the table.

[0042]

[Table 4]

[0043]

[Table 5]

[0044]

As described above, LiNiO ₂ or LiNi _1-x M _x O ₂ powder [where 0 <x ≦ 0.
4, M = Co, Mn, B, Al, V, P, Mg, Ti). The positive electrode active material for a lithium secondary battery of the present invention has a sulfur content of 0.5% by weight or less. Therefore, since the growth of the crystal is not hindered, it is effective in increasing the primary particle diameter and reducing the specific surface area, and when incorporated in a battery, a high initial capacity can be obtained.

The active material whose specific surface area is adjusted so as not to exceed a predetermined value of 0.5 m ² / g has good storage stability as battery characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a coin battery prepared as a test battery in Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stainless steel case 2 Gasket 3 Sealing plate 4 Negative electrode 5 Positive electrode 6 Separator 7 Negative electrode collector 8 Positive electrode collector

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koichi Chori 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Yuichi Ito 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (56) References JP-A-4-2499073 (JP, A) JP-A-8-319120 (JP, A) JP-A-9-231973 (JP, A) (58) Fields surveyed ( Int.Cl. ⁷ , DB name) H01M 4/58 H01M 4/02 H01M 10/40

Claims (6)

(57) [Claims] 1. LiNiO ₂ powder or LiNi
_1-x M _{x O 2} powder [where, 0 <x ≦ 0.4, M = C
o, Mn, B, Al, V, P, Mg, at least one of Ti]
A positive electrode active material for a lithium secondary battery, wherein the sulfur content in the material is 0.5% by weight or less. 2. LiNiO ₂ powder or LiNi
_1-x M _{x O 2} powder [where, 0 <x ≦ 0.4, M = C
o, Mn, B, Al, V, P, Mg, at least one of Ti]
The positive electrode active material for a lithium secondary battery, wherein the sulfur content in the powder is 0.5% by weight or less and the specific surface area of the powder is 0.06 to 0.46 m ² / g . 3. The method according to claim 1, wherein said sulfur content is 0.01% by weight or less.
The positive electrode for a lithium secondary battery according to claim 1 or 2,
Extremely active material . 4. LiN having a sulfur content of 0.5% by weight or less
iO ₂ powder or LiNi _1-x M _x O ₂ powder [where 0 <x ≦ 0.4, M = Co, Mn, B, Al, V,
Or more of P, Mg, and Ti] as a positive electrode active material, and a positive electrode mixture obtained by kneading a conductive agent and a binder into the positive electrode active material. 5. A sulfur content of 0.5% by weight or less,
Li having a specific surface area of 0.06 to 0.46 m ² / g
NiO ₂ powder or LiNi _1-x M _x O ₂ powder [where 0 <x ≦ 0.4, M = Co, Mn, B, Al,
V, P, Mg, or Ti] as a positive electrode active material, and incorporating a positive electrode mixture obtained by kneading a conductive agent and a binder into the positive electrode active material. 6. When the sulfur content is 0.01% by weight or less.
The lithium secondary battery according to claim 4 or 5, wherein